An oil and gas well may be drilled with drill pipe to a certain depth. Casing may thereafter be run and cemented in the well. An operator may then continue to drill the well to a greater depth with drill pipe and cement in still another string of casing. In this type of system, each string of casing may extend to a surface wellhead assembly.
In some well completions, an operator may install a liner rather than a string of casing. The liner may be made up of joints of pipe in the same manner as casing, and may also be cemented into the well. The liner, however, may not extend back to the surface wellhead assembly. Instead, the liner may be secured by a liner hanger to just above a lower end of the last string of casing. To cement the liner, the operator may set the liner hanger and pump cement through the liner, such that the cement may flow into an annulus between the liner and the well.
In some drilling scenarios, when installing a liner, the operator may drill the well to a certain depth using a drill string, retrieve the drill string, and then assemble and lower the liner into the well. In other scenarios, the operator may run the liner while drilling the well.